Study of complex formation between 18-crown-6 and diaza-18-crown-6 with uranyl cation (UO2 2+) in some binary mixed aqueous and non-aqueous solvents

The complexation reaction between UO2 (2+) cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile-methanol (AN-MeOH), nitromethane-methanol (NM-MeOH) and propylencarbonate-ethanol (PC-EtOH) binary mixed systems at 25 A degrees C. In addition, the complexation process between UO2 (2+) cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-ethylacetate (AN-EtOAc), methanol-water (MeOH-H2O), ethanol-water (EtOH-H2O), acetonitrile-water (AN-H2O), dimethylformamide-methanol (DMF-MeOH), dimethylformamide-ethanol (DMF-EtOH), and dimethylformamide-ethylacetate (DMF-EtOAc) binary solutions at 25 A degrees C using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between (18C6) and (DA18C6) with UO2 (2+) cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L-2] complex is formed in solutions. The values of stability constants (log K-f) of (18C6 center dot A UO2 (2+)) and (DA18C6 center dot A UO2 (2+)) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions. In all cases, a non-linear relationship is observed for the changes of stability constants (log K-f) of the (18C6 center dot A UO2 (2+)) and (DA18C6 center dot A UO2 (2+)) complexes versus the composition of the binary mixed solvents. The stability order of (18C6 center dot A UO2 (2+)) complex in pure studied solvents was found to be: EtOH > AN a parts per thousand NM > PC a parts per thousand MeOH, but in the case of (DA18C6 center dot A UO2 (2+)) complex it was : H2O > MeOH > EtOH.